Method and device for drawing metal cups to can bodies

ABSTRACT

A method for drawing metal cups to can bodies has the steps of drawing the cups through several roll collars while spraying a lubricant in such a way that it lubricates the roll surfaces, the can body and the roll bearings, and also cools, and flushes fine substances. The device for the method has roll collars, a mandrel, ducts connected to a source of lubricant, and orifices for directing the lubricant in spray jets.

United States Patent l i l 1 inventor Appl. No Filed Patented AssigneePriority Wilhelm Friedrich Lauener Langenhard, Switzerland 758,389

Sept. 9, 1968 June 1, 197 1 Prolizenz AG Chur, Switzerland Sept. 7, 1967Switzerland METHOD AND DEVICE FOR DRAWING METAL 10/1944 Orr et al.7/1964 Properzi 7/1968 Calmes.......

12/1934 Dahl et al. .i 2/1943 Wilke et al References Cited lTED STATESPATENTS F ORElGN PATENTS Italy Great Britain Primary ExaminerCharles W.Lanham Assistant Examiner-E. M. Combs AtlorneyErnest F. Marmorek 38' m4, Z2 39 32 a4 I r l 25 1a 1 /9 rs PATENIED JUN 1 1971 SHEEI 1 UF 2IVIII/IIIIVIIIIIII //IIIIIIIIIIIIIIIIIII I I I I I I I I I I I I I IFig.1

METHOD AND DEVICE FOR DRAWING METAL CUPS T CAN BODIES The presentinvention relates to a method for drawing metal cups to can bodies andto a device for carrying out the method.

Tinplate can bodies are generally made by rolling up a blank of tinplateto a hollow cylinder, soldering the abutting longitudinal edges andsecuring a bottom. Attempts have, however, been made to produce seamlesscan bodies by roll-bond methods; the bottom, nevertheless, still neededto be secured separately.

In the field of the manufacture of can bodies, aluminum and its alloysare of increasing importance, as the bodies made from them presentsubstantial advantages over the bodies made from tinplate; theadvantages include: light weight, absence of rusting danger, manypossibilities of opening without use of any special tool, and so on. Agreat advantage of the light metal can bodies is that they can be madeby deep drawing or impact extrusion in one piece and seamless; thereremains only the operation to affix the cover in a convenient manner,for instance by a folding border and a sealing ring, or by means of anadhesive, and so on.

For the manufacture of light-metal can bodies one uses generallyunalloyed aluminum sheet. The can bodies made therefrom have usually awall thickness of from 0.2 to 0.5 mm.; for aerosol cans a thicker wallis needed, for instance of 0.8 mm. In competition with tin cans it wouldbe necessary in several cases to use an aluminum sheet of such a greatthickness for obtaining the same buckling strength that the aluminum canwould not be competitive because of its price.

A higher buckling strength may be obtained by using an aluminum alloyinstead of unalloyed aluminum, as the alloys have a higher mechanicalstrength. Then it would be possible to make the wall thinner, so thatthe cost of the can would be lowered and it would be possible tocomplete with the tinplate can.

The aluminum alloys AlMg2,* AlMg2,='-* AlMn with 1.5% Mn*** and AlMnMgwith 1% Mn and 1% AA No. 5009 and 50s 1. AA No. 5252. 5452. 5852. ***AANo. 3003. AA No. 3004.

could be taken into consideration. In the cold worked state these alloyshave a tensile strength which surpasses substantially that of coldworked unalloyed aluminum. The 3 aforementioned alloys are composed ofaluminum with a low content of alloying elements: in contrast to thealloys AlMgSi,* AlCuMg** and AlZnMg""- for instance, they can i AA6000-Series AA 2000-Series. AA 7000-Series. be hardened only by coldworking, but not by heat treatment (solution annealing, quenching andnatural or artificial aging); the manufacture of can bodies fromheattreatable alloys is possible, but the necessary heat treatment makesthe man-= ufacture more difficult and more expensive.

According to known deep drawing methods for making thin-walled aluminumcans, two successive operational steps are carried out, namely theforming of a cup from a disc by deep drawing and immediately afterwardsand in the same machine the thinning of the wall by drawing the formedcup through a number of lubricated dies. According to that method it ispossible to make at most 50 to about 100 can bodies from unalloyedaluminum per minute. This method applied to the manufacture of canbodies from aluminum alloys has not until now yielded any satisfactoryresult.

The difficulties encountered with the last method are caused chiefly bythe friction and the heat developed in the drawing dies; after severaldrawing operations a localization of heat takes place, and the lubricantfilm becomes ruptured.

Furthermore, the method is very much influenced by small variations ofthe uality of the discs, for instance of their thickness, of the grainsize of the sheet of the disc and of its texture. Finally, the mentionedmethod is only applicable to the working of unalloyed aluminum, withoutregard to the fact that when cans are made from aluminum with a lowcontent of alloying elements, for example from the alloy A1Mg or AlMg itis desirable, for the aforementioned reasons of economics, to decreasefurther the wall thickness of the finished cans.

Numerous attempts have shown that the manufacture of seamless can bodiesin one piece from aluminum with a low content of alloying elements(AlMg; for instance) cannot be carried out according to most of theusual methods of deep drawing.

During the reduction of the thickness by drawing through one or severaldies the material becomes brittle in consequence of excessive coldworking and the wall of the can body tears. Theoretically it would bepossible to avoid brittleness by means of one or more intermediateannealings, but

such a complicated method is not any more practical than hot drawing.

It is accordingly among the principal objects of the invention toprovide a method and a machine for making one-piece metal cups whichavoid the drawbacks of the prior art.

Further objects and advantages of the invention will be set forth inpart in the following specification and in part will be obvioustherefrom without being specifically referred to, the same beingrealized and attained as pointed out in the claims hereof.

According to the invention the difficulties of manufacturing can bodiesfrom aluminum alloys are overcome by substituting a rolling operationfor the drawing operation, in which rolling operation the tool surfaceswhich reduce the wall thickness move in the same direction as the canwall to be drawn, so that no substantial reciprocal movement takes placebetween the wall of the can body and the surface of the tool. Therolling operation may be completed by the usual drawing operation(through drawing dies).

The method according to the invention comprises drawing (elongating)metal cups, for instance of aluminum or preferably of aluminum alloys,by means of a number of drawing-roll collars and a drawing mandrel,while spraying a diluted lubricant preferably an emulsion of oil inwater, in such a manner against the periphery of the drawing rolls thatthe diluted lubricant does not only lubricate the outer forming surface(periphery) of the rolls and the outer surface of the hollow body to bedrawn, but also has a cooling effect and flushes away fine wearparticles and other substances.

The roll collar" or drawing-roll collar is an annular tool comprising aseries of separately mechanically adjusted rolls acting radially againsta mandrel on which a hollow body is pushed through the rolls. Theperiphery of the rolls is concave in order to fit to the convexity ofthe hollow body to be drawn. Such a roll collar is represented, forinstance, in FIG. 9 of US. Pat. No. 2,361,318 and in FIG. 4 of thepresent application.

Emulsions of from about 2 to about 10 percent by volume of oil in waterhave been found to be advantageous as lubricant for the instant purpose.

According to a preferred embodiment the lubricant is directed in form ofjets against the rolls under such an angle that the rolls are put inmotion in that sense of rotation which corresponds to the direction ofmovement of the can body during drawing; the jets must therefore impingeexcentrically on the roll periphery.

It is known to reduce the wall thickness of relatively thickwalled tubesby means of one or more roll collars. For instance, the German Pat. No.890,937 shows a drawing-roll collar for the cold drawing of tubes whichcomprises three or preferably four rolls of small diameter resting upona corresponding number of supporting rolls of greater diameter. Thepublished German Pat. application No. 1,040,994 describes a similar toolhaving drawingroll collars which comprise each five to seven rolls,preferably six rolls. According to the US. Pat. No. 2,361,318 a seamlesssteel tube becomes stretched through a drawing-roll collar until it hasa wall thickness of 13 mm. with an outer diameter of 290 mm.; the ratioof the wall thickness to the outer diameter is therefore about 4.5percent (4.5 100). The number of rolls amounts to eight for each collarand there may be used one to ten or more collars, but preferably two orthree.

It seemed from the first rather doubtful whether one would succeed indrawing cups to extremely thin-walled cylindrical cans by means ofroll-collars, that is to say by a method which has been applied up tonow only for elongating thick-walled tubes.

The difference between iron and steel tubes used for water pipes and soon, on one hand, and can bodies for packing purposes, on the other hand,is extremely great regarding the wall thickness involved. Foraluminum-alloy can bodies ofa diameter of 50 to 120 mm., for instance, awall thickness of from I about 0.15 to 0.3 mm. may be considered; theratio ofthe wall thickness to the outer diameter is therefore about 0.3to 0.25 percent (0.30.25: 100).

Moreover, the working speed in connection with the can body manufactureexceeds many times that of the steel tube elongating. ln the drawing ofcan bodies the mandrel needs to execute about 1 to reciprocating strokesper second. The working speed of the mandrel amounts therefore to about100 to 500 meters per minute. The moving direction changes from 120 to600 times during this period.

Another substantial difference between the elongating of tubes and thedrawing of can bodies consists in the fact that tubes are open at bothends whereas can bodies which are drawn from cups have a bottom and aretherefore open only at one end. The great importance of this differencewill be pointed out further below.

According to the method of the invention, one may elongate by 2 to 4times cups made not only from aluminum alloys and from unalloyedaluminum, but also from other workable metals, including steel, formanufacturing for instance can bodies with a diameter of from about 50to about 100 mm. and a length of from about 100 to about 350 mm.

The instant invention is particularly suited for the manufacture of canbodies for beer cans (length 140 mm.), food cans (length 120 mm.) andaerosol cans (length at present up to 340 mm.) from aluminum alloys.

When carrying out the method according to the invention the initial wallthickness of the cylindrical part amounts at the most to 3 percent ofthe inner diameter of the hollow body; but preferably to 1.5 percent orless.

The device or machine for carrying out the method accord ing to theinvention includes several drawing-roll collars, a drawing mandrel knownper se and lubrication ducts, the discharge orifice of which beingdirected against the forming surface (periphery) of the rolls and whichare connected to a source of lubricant under pressure; the device ispreferably disposed vertically, the free end of the mandrel beingdirected upwardly.

The equipment for supplying the cups and for stripping off the elongatedcan bodies by means of compressed air or other compressed gas ormechanically is of conventional construction', likewise conventional isthe counterpunch with which the device is preferably equipped and thepurpose of which is chiefly to form the bottom of the can body to thedesired shape respectively to provide a stamping or a protruding plug.

In contrast to the known machines for stretching relatively thick-walledtubes, the ratio of the diameter of the rolls of the device according tothe invention relative to the wall thickness of the hollow body, is ofgreat importance ifa counterpunch is used: as the can bodies have abottom which, during the elongating operation or better just after thesame, will be shaped for instance vaulted or stamped in the device.

The bottom of the can body must therefore remain in contact with thefront end of the mandrel, as the latter together with the counterpunchmust serve as a forming, respectively stamping tool. Any forwardslipping of the bottom of the can body must be avoided during drawing(elongating) and the bottom of the body must not be loosened from thefront end of the mandrel. Otherwise it would not be possible to carryout the desired forming respectively stamping, and the bottom wouldbecome squashed in consequence of the resulting cavity. When stretchingsteel tubes and the like, this problem does not arise and a possibleforward slipping of the hollow body there would not disturb theoperation.

According to a further embodiment of the invention, the forward slippingis avoided by choosing accurately the diameter of the rolls relative tothe wall thickness of the hollow bodies. The diameter of the rolls mustnot be smaller than 50 times the final wall thickness of the can bodyand not larger than 300 times; it is preferably from to 250 times largerthan the rolled wall thickness. For instance, when manufacturing canbodies from aluminum alloy with a wall thickness of (H5 to 0.3 mm. (thediameter of the can being 50 to mm. for example), one uses suitablyrolls of a diameter of from 15 to 80 mm. The diameter of the rolls doesnot depend on the diameter of the can body. For a wall thickness of 0.2to 0.5 mm. the diameter of the rolls is preferably from 45 to 50 mm.',for a wall thickness of 0.8 mm., for instance, one could get along witha roll diameter of 60 mm., but one should manage for a smaller reductionin thickness in each roll collar, because too great a reduction leads tothe formation of too great fins. Accordingly, one must take inconstructing the device for carrying out the method according to theinvention that the rolls have a diameter of 50 to 300 times, preferablyof 100 to 250 times the smallest clearance between the roll peripheryand the surface of the mandrel, the said clearance being substantiallyuniform on the whole circumference of the mandrel.

It may be advantageous to diminish the roll diameter from one rollcollar to the next in the drawing direction.

When reducing the wall thickness of a cylindrical hollow body, ribs(fins) are formed between the rolls of the drawing tool in the drawingdirection. This involves the necessity in the manufacture of hollowbodies having a smooth surface to use at least two roll collars, therolls of them being offset from one collar to the other in such a waythat at the passage through the second roll collar the fins formed bythe first collar are flattened out. The clearance between two laterallyadjacent rolls should be as small as practicable so that the formed finsare as small as possible. The clearance should be less than 0.3 mm.,preferably 0.2 mm. or less.

Generally, the wall thickness will not be reduced as much as desired inthe first roll collar. Therefore, the second roll collar must not onlysuppress the fins produced by the first one, but also reduce thethickness of the remainder of the wall. In this case a third roll collaris necessary or at least desirable, the purpose of which is again aswell to flatten the fins as to reduce further the wall thickness. Thenumber of the roll collars may exceed four and may amount, for instance,to 10. The number of roll collars should only be as large as absolutelynecessary, as the difficulties of construction increase with the numberof the roll collars because of the length of the stroke of the mandrel;the mandrel performing the drawing must pickup the cup at the inlet ofthe drawing device and project beyond the other end of the drawingdevice far enough so that the drawn hollow body may be removed easily.For the manufacture of beer cans of a height of about mm. and a diameterof 65 mm., the mandrel must have a stroke of 650 mm.

In order to obtain the final smoothing of the can body before leavingthe drawing device it is suitable, but not indispensable, to disposenear the outlet of the device instead of a roll collar one or morenormal drawing dies, for instance self-centering dies, with polishedworking surface.

Thorough investigations have shown that for the drawing of can bodieseach roll collar must have at least 10 rolls, preferably 12 or more.Generally one would, for the same precision of the surface of the rollsand for the same material of the hollow body, choose a number of rollsthat increases with a decrease in the ratio of the wall thicknessrelative to the diameter of the hollow body. For instance, a roll collarfor the manufacture of cans of an aluminum-magnesium alloy containlngabout 2 percent Mg with a wall thickness of 0.2 mm. and a diameter of 65mm. is provided according to the invention with from 12 to 18 rolls.

Considering the extremely thin wall of the drawn can body (for instance0.2 to 0.3 mm.) one realizes immediately that extremely great emphasismust be put on the precision of the guiding of the mandrel, which cannotbe compared with the guiding of a mandrel while stretching relativelythick-walled tubes, for example ofiron or steel.

The known machines with roll collars for stretching tubes are disposedhorizontally. Also most devices for drawing can bodies are disposedhorizontally. However, the tests and research which led to theconstruction of the can-body drawing-device according to the inventionhave shown that the new device should preferably be disposed verticallyor almost ver tically, otherwise the long shaft of the mandrel, due toits own weight, would have the tendency to be bent against the lowerdrawing rolls. Although such a deflection can be kept extremely small,the difference of wall thickness (in cross section through the can body)caused by the deflection may nevertheless be important because of theextreme thinness of the wall. These considerations also militate againstan inclined mounting of the device.

When mounted vertically or substantially vertically, the drawing devicecan be disposed either in such a way that the mandrel pushes the cupdownwards through the roll collars, and the can body leaves the tool atthe bottom, or in such a way that the mandrel pushes the cup upwards.The last disposition is by far the most advantageous because of thelubricating according to the invention.

Thorough tests have proved that sliding bearings are poorly suitable forthe rolls of the device according to the invention, and only rollerbearings are adequate. Needle bearings are preferred, because of thespace available for the bearings is small.

In one and the same collar the rolls need not all have the samethickness. The ring may, if desired, be equipped with alternating thinand thick rolls.

The outlet diameter of the lubricant ducts, which are directed againstthe periphery of the rolls, must be so narrow that the diluted lubricantunder the applied pressure impinges with a strong jet on the rolls. Thespeed of the lubricant jet may be to meters per second with an emulsionof oil in water under an atmospheric excess pressure of 2 to S and alubricant duct outlet diameter of about 1 mm.

If the lubricant jets impinge eccentrically on the periphery of thefreely rotating rolls, the latter get a supplementary propulsion thatmakes possible a considerable increase of the number of strokes.

The instant lubricating system favors the instant vertical arrangeinentof the machine. Ifthe device had instead a horizon' tal or an inclinedposition, the unilateral flow of the lubricant would have thetroublesome consequence that dirt would enter temporarily the bearingsof the rolls of the different collars and would disturb the operation;the high working speed of the device and the extreme thinness of the canbody wall could not tolerate such disturbances. Also this problem doesnot arise with the known stretching of tubes by means of rollcollars.With the method according to the invention, however, the mentioneddanger of disturbances is a further ground for the preferred choice ofthe substantially vertical disposition of the device.

Furthermore, the lubricating system according to the invention is bestsuited for the arrangement where the vertical mandrel pushes the hollowbody upwards. The lubricant which streams in the drawing device will becollected at the bottom, filtered and put again into circulation. If thecan bodies would leave the drawing device at the bottom, they wouldcarry away a part of the streaming lubricant, as one should strip themaway with the bottom down; there would result a serious disturbance ofthe lubricant circulation, besides the greater difficulty in ejectingthe elongated can bodies.

With the device according to the invention the stripping of the canbodies is done in a known manner either by compressed air supplied tothe mandrel through a longitudinal bore hole, or mechanically; then thecan bodies are suitably blown away in a known manner by a lateralairjet.

In the drawings,

FIG. I is vertical sectional view of a cup (from which the can body willbe produced);

FIG. 2 is a fragmentary sectional view showing the cup of FIG. I beingoperated on;

FIG. 3 is vertical sectional view of a machine for producing a can bodyfrom the cup of FIG. I; and

FIG. 4 is a sectional view taken on the line 4-4 of FIG. 3.

The cup 10 according to FIG. I is obtained by deep drawing or by anyother method. According to the invention the cup is pushed by means of amandrel 11 (FIG. 2) through one or more roll collars 12, whereby itswall becomes stretched and thinned; the drawing tool representedschematically comprises substantially a collar of rolls l3 and trunnions14.

The device according to FIGS, 3 and 4 comprises four superposed rollcollars 17 in a housing 15 resting on a base 16. The roll collars 17 areeach provided with twelve forming rolls l8 rotating on needle bearings19. The supports 20 lean against the cylinder wall 21 without clearance.The distance of the periphery of the rolls 18, that is to say of theirforming surface, to the mandrel 22 is, for instance, 0.45 mm. at thelower roll collar. This distance diminishes from collar to collar and isat the upper collar for instance only 0.25 mm. In this case the wallthickness of the cup will be reduced for instance from 0.6 mm. to 0.25mm.

The ring conduits 23 serve to supply lubricant to the bore holes 24,which operate as lubricant ducts. The orifices of the lubricant ductshave nozzles 25 which are directed eccentrically against the rolls 18.The splashing lubricant thus not only lubricates the forming surfaces ofthe rolls, the outer surface of the body to be drawn and the bearings 19of the rolls, effects a cooling, and flushes away fins and other dirt,but also that there will be rotated the rolls 18 in such a way thattheir forming surface moves upward at the side facing the mandrel 22.

For the final smoothing of the outer surface of the can body two usualdrawing dies 26 and 27 are shrunk in bushings 28 or 29 over the rollcollars 17. The intermediate ring 30 is not absolutely necessary; itenables the subsequent mounting of a further roll collar or a furtherdrawing die. The enlarged space 31 at the inner lower part of thelubrication ring duct 32 serves to collect lubricant sprayed through thering duct 33 and the bore holes 34 against the surface of the can body;the collected lubricant flows through the ring like recess 35 and thebore holes 36 into the inside of the drawing device.

The drawing mandrel 22 is screwed into the upper end of the shaft 37which is operated by a drive disposed underneath (not shown). It isprovided with a recess 38 which in cooperation with the bottom face 39of the counterpunch 40 imparts to the bottom of the can body the desiredvaulted shape.

In this example, the counterpunch 40 is driven in a known manner; a coilspring would be sufficient. A down holder 41 bears elastically on thecoil spring 42. When the tool ends 38 and 39 meet one another, thepressure deforms the bottom of the can bodies as desired.

The lateral supply of compressed air for blowing away the can bodiesafter stripping from the mandrel 22, and the drive of the shaft 37, arewell known and hence not shown.

I wish it to be understood that I do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

Having thus described the invention, what I claim as new and desire tobe secured by Letters Patent, is as follows:

I. A method for drawing can bodies from metal cups, comprising the stepsof placing a cup over a mandrel and forcing it upwardly through severaldrawing-roll collars, each collar being provided with a plurality offorming rolls, while directing a pressurized diluted lubricant spray injets eccentrically or tangentially against the periphery of the rolls ofeach collar and putting them in motion in that sense of rotation whichcorresponds to the direction of movement of the can body during drawing,whereby the forming rolls of each collar receive ad ditional propulsionby the eccentrically applied lubricant spray, and the forming surfacesofsaid rolls, the outer surfaces of the can body to be drawn, and theroll bearings are cleaned, cooled, and lubricatedv 2. A substantiallyvertically disposed device for drawing can bodies from metal cups, saiddevice comprising at least two drawing-roll collars, each collar beingprovided with a plurali ty of forming rolls, said collars being pivotedon needle bearings, 21 mandrel having an upwardly directed frontsurface, a plurality of ducts having orifices and being connected to asource of lubricant under pressure, the orifices of said ducts beingarranged direct jets of pressurized lubricant eccentrically ortangentially against the peripheries of the rolls of each collar forputting the rolls in motion in that sense of rotation which correspondsto the direction of the can body during drawing, whereby the formingrolls of each collar receive additional propulsion by the eccentricallyapplied lubricant spray, and the forming surfaces of said rolls, theouter surfaces of the can body to be drawn, and the roll bearings arecleaned, cooled, and lubricated.

3. A device according to claim 2, the diameter of the rolls being from50 to 300 times the smallest uniform clearance between the periphery ofthe rolls and the surface of the mandrel.

4. A device according to claim 2, the diameter of the rolls being fromI00 to 250 the smallest uniform clearance between the periphery ofthcrolls and the surface of the mandrel.

5. A device according to claim 2, each drawing-roll collar carrying atleast 10 rolls.

6. A device according to claim 2, each drawing-roll collar carrying froml2 to 18 rolls.

7. A device according to claim 2, comprising at least one drawing diethrough which the can body is pushed at the termination of theelongation of said body.

1. A method for drawing can bodies from metal cups, comprising the stepsof placing a cup over a mandrel and forcing it upwardly through severaldrawing-roll collars, each collar being provided with a plurality offorming rolls, while directing a pressurized diluted lubricant spray injets eccentrically or tangentially against the periphery of the rolls ofeach collar and putting them in motion in that sense of rotation whichcorresponds to the direction of movement of the can body during drawing,whereby the forming rolls of each collar receive additional propulsionby the eccentrically applied lubricant spray, and the forming surfacesof said rolls, the outer surfaces of the can body to be drawn, and theroll bearings are cleaned, cooled, and lubricated.
 2. A substantiallyvertically disposed device for drawing can bodies from metal cups, saiddevice comprising at least two drawing-roll collars, each collar beingprovided with a plurality of forming rolls, said collars being pivotedon needle bearings, a mandrel having an upwardly directed front surface,a plurality of ducts having orifices and being connected to a source oflubricant under pressure, the orifices of said ducts being arranged odirect jets of pressurized lubricant eccentrically or tangentiallyagainst the peripheries of the rolls of each collar for putting therolls in motion in that sense of rotation which corresponds to thedirection of the can body during drawing, whereby the forming rolls ofeach collar receive additional propulsion by the eccentrically appliedlubricant spray, and the forming surfaces of said rolls, the outersurfaces of the can body to be drawn, and the roll bearings are cleaned,cooled, and lubricated.
 3. A device accOrding to claim 2, the diameterof the rolls being from 50 to 300 times the smallest uniform clearancebetween the periphery of the rolls and the surface of the mandrel.
 4. Adevice according to claim 2, the diameter of the rolls being from 100 to250 the smallest uniform clearance between the periphery of the rollsand the surface of the mandrel.
 5. A device according to claim 2, eachdrawing-roll collar carrying at least 10 rolls.
 6. A device according toclaim 2, each drawing-roll collar carrying from 12 to 18 rolls.
 7. Adevice according to claim 2, comprising at least one drawing die throughwhich the can body is pushed at the termination of the elongation ofsaid body.